Abstract
The effect of CoO doping on the microwave dielectric property and the microstructure of (Y 2− x Sm x )BaCuO 5 ceramics have been investigated. The limits of the (Y 2− x Sm x )Ba(Cu 1− y Co y )O 5 ( x =0,1 and 2) solid solutions were approximately y =0.1 and the deviations of the valences in cations determined by using bond valence sum may be related to the formation of the solid solutions. It was found that high Q · f values were obtained by the Co substitution for Cu in the (Y 2− x Sm x )BaCuO 5 ceramics, whereas the τ f values were not improved. In the Sm-substituted (Y 2− x Sm x )Ba(Cu 1− y Co y )O 5 ceramics, the optimum value of τ f which was closest to 0 ppm/°C was −6.3 ppm/°C for x =2. The reduction of porosity in the Sm 2 Ba(Cu 1− y Co y )O 5 ceramics at compositions lower than y =0.01 was recognized; it was found that these morphological changes in the ceramics were closely related to the increase of the Q · f values. Thus, the optimum dielectric properties, i.e. ε r =16.8, Q · f =90732 GHz and τ f =−9.2 ppm/°C, were obtained in the Sm 2 Ba(Cu 0.99 Co 0.01 )O 5 ceramics by using cold isotropic pressing (CIP).
Published Version
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